Electrically reconfigurable optical devices

ABSTRACT

The invention refers to electrically reconfigurable optical devices based on the use of a layer of dielectric and transparent viscoelastic material (G) opposing at least a first electrode structure (ES 1 ). According to the invention the arrangement of the individual electrode zones in the first electrode structure (ES 1 ) in order to deform the viscoelastic layer (G) complies with one of the following alternatives. According to the first alternative, the electrode zones of the first electrode structure (ES 1 ) are grouped into groups composed of two or more adjacent electrode zones and within each of said groups individual electrode zones are supplied each with a substantially different voltage. According to the second alternative, the electrode zones of the first electrode structure (ES 1 ) are substantially annular, elliptical, rectangular or polygonal closed-loop electrodes. The invention allows, for example, for creating electrically reconfigurable blazed gratings ( 30 ) or Fresnel zone lenses ( 40 ).

[0001] The present invention relates to electrically reconfigurableoptical devices according to the preamble of the appended claim 1. Theinvention also relates to a method for forming electricallyreconfigurable optical devices according to the preamble of the appendedclaim 8.

[0002] Optical signals in different forms are today increasinglyutilized in many different types of devices and applications. In orderto take full advantage of systems including optical signals or beams, itmust be possible to direct the optical signal or beam coming in on aguided optical conduit, or on some other type of optical system in adesired electrically controlled manner to another optical conduit or toanother optical system. The aforementioned optical conduit can be, forexample, an optical fiber or other type of optical waveguide. On theother hand, the optical signals or beams can be passed through, betweenor out of optical systems, which systems consist entirely or partly, forexample, of more traditional lenses and/or other optical components,which may be separated by air or another optically transparent medium.In between the aforementioned applications there are a wide variety ofoptical systems, which work under fast changing operational conditions,and thus require the capability to perform optical functions in anefficient and electrically controlled manner.

[0003] Especially the recent rapid development of opticaltelecommunication and optical data processing systems creates increasingneeds for versatile electrically reconfigurable optical devices.

[0004] In addition to the act of simply switching the opticalsignal/beam on or off, the term “optical switching” hereinbelow alsorefers to more complex optical functions, i.e. transformations of theoptical signal/beam and/or its path. These include, for example,dividing, redirecting, wavelength filtering or focusing the opticalsignal/beam in a desired manner. Optical switching can thus be used tomodulate a light beam by altering the amplitude, spectrum or phase ofthe light.

[0005] In the following, some prior art solutions for electricallycontrolled optical switching are shortly discussed. However, suchmethods, which are based on first converting optical signals intoelectrical signals for switching and then reconverting said electricalsignals back into optical signals for outputting, are not included inthe following discussion as they are not relevant to the presentinvention.

[0006] A conventional method for electrically controlled opticalswitching is to mechanically move the optical components, for examplemirrors, beamsplitters or filters in order to affect the propagation ofthe optical signal/beam. Said mechanical movements can be realized usingvarious kinds of electrical actuators. However, such optical componentstogether with the required electrical actuators cannot be easily madevery compact in size and they are also rather difficult and expensive tomanufacture, especially as mass-produced articles.

[0007] Silicon-surfacemicromachining is a recent technology forfabricating miniature or microscopic devices. This technology has alsobeen used for manufacturing optical microelectromechanical systems(optical MEMS).

[0008] U.S. Pat. No. 5,867,297 discloses an oscillatory optical MEMSdevice including a micromirror for deflecting light in a predeterminedmanner. Small physical sizes and masses of these micromachined silicon“machine parts” make them more robust and capable of faster operationthan conventional macroscopic mechanical devices.

[0009] Grating Light Valve™ devices by Silicon Light Machines, USArepresent another type of optical MEMS devices. U.S. Pat. No. 5,311,360discloses a light modulator structure, which consists of parallel rowsof reflective ribbons. Alternative rows of ribbons can be pulled down byelectrostatic attraction forces a distance corresponding toapproximately one-quarter wavelength to create an electricallycontrolled grating like structure, which can be used to diffractivelymodulate the incident light wave. The electrical switching of theribbons can be realized by integrating bottom electrodes below theribbons, and by applying different voltages to the ribbons and saidbottom electrodes to create the required electrostatic forces. U.S. Pat.No. 6,130,770 discloses another type of solution, where instead of usingphysical electrical connections to charge the predetermined ribbons ofthe light modulator structure, selected ribbons are electrically chargedwith an electron gun.

[0010] In principle, silicon optical MEMS technology uses processingsteps derived from the integrated circuit (IC) fabrication techniques ofphotolithography, material deposition and chemical etching to producethe movable mechanical structures on a silicon chip. The aforementionedmanufacturing process is, however, fairly difficult and thus expensive.Further, the optical MEMS devices operate mainly only in reflection andthus the capability of such devices of more complex transformations ofthe optical signal/beam and/or its path are limited. Material fatiguemay also become significant in certain applications.

[0011] Birefringence, also known as double refraction, is a propertywhich can be found in some transparent materials, for example incrystals. Such optical materials have two different indices ofrefraction in different directions. This can be used to create Pockelseffect, an electro-optical effect in which the application of anelectric field produces a birefringence which is proportional to theelectric field applied to the material. The Pockels effect is well knownin the art and it is commonly used to create, for example, fast opticalshutters. However, because the use of birefringence requires use ofpolarized light, this severely limits its use as a general method inrealizing optical switching devices.

[0012] U.S. Pat. No. 5,937,115 describes switchable optical componentstructures based on a holographic polymer dispersed liquid crystal.These are electronically controlled Bragg grating structures which allowto electronically switch on and off the diffractive effect of thetransparent grating structures, which have been optically recorded orotherwise generated in the material. These electronically switchableBragg grating (ESBG) devices can be used for various filtering orlensing applications. The major drawback of the ESBG technology is thecomplex manufacturing process required. Environmental concerns andhazards generally related to liquid crystal materials apply, naturally,also to the ESBG devices.

[0013] U.S. Pat. No. 4,626,920 discloses a semiconductor device, whichhas an array of spaced charge storage electrodes on semiconductormaterial (Si) and an elastomer layer disposed on said electrodes. Atleast one conductive and light reflective layer is disposed over theelastomer layer. When voltages are applied between the charge storageelectrodes and the conductive layer, this causes the deformation of theconductive/reflective layer and the elastomer layer from a flat surfaceto a form having a sinusoidally cyclically varying cross-section. Thus,the reflective front surface of the conductive layer can be utilized asan electrically switchable reflective grating.

[0014] GB patent 2,237,443 describes another light modulating device,where a reflective elastomer or viscoelastic layer is utilized for lightmodulation. In this arrangement an electron gun (cathode ray tube) isused instead of direct electrical connections/electrodes (cf. U.S. Pat.No. 4,626,920) to generate the electrical pattern needed to deform theelastomer layer.

[0015] An important aspect in the above described type of systems (U.S.Pat. No. 4,626,920 and GB 2,237,443) is the operation of theconductive/reflective layer or layers which is/are mounted on thedeformable elastomer layer. Said conductive/reflective layer or layersmust reliably and repeatably provide precise patterns of deformationswhich correspond to the charge pattern modifying the elastomer layer.This, together with the fact that said devices operate only inreflection, limits the use of such devices due to the limited selectionof suitable conductive and reflective materials as well as due to theoverall response characteristics (sensitivity to the appliedvoltages/charges, temporal response characteristics) of the device.

[0016] Yury P. Guscho “Physics of Reliofography” (Nauka, 1992, 520 p. inRussian) describes in chapter 7 a number of light modulator structures,in which a transparent viscoelastic layer is electrically deformed tomanipulate the light passing through said viscoelastic layer. Thesedevices can be taken to present the closest prior art with respect tothe current invention, and they are therefore shortly described belowwith reference to the appended FIGS. 1a and 1 b.

[0017]FIGS. 1a and 1 b correspond to FIG. 7.1 in chapter 7 of “Physicsof Reliofography” and show the two basic schemes of the light modulatorstructures.

[0018] In the first scheme in FIG. 1a, the driving signal for deformingthe viscoelastic layer G is applied from the free side of theviscoelastic layer G using driving electrodes ES1, which electrodes ES1are formed on the lower surface of a top glass substrate SM1. A gap isleft between the free surface of the viscoelastic layer G and the lowersurface of the top glass substrate SM1, allowing the viscoelastic layerG to deform without contacting the opposite structure. Theaforementioned gap can be for example air, gas or vacuum. The electricfield deforming the viscoelastic layer G is generated between thedriving electrodes ES1 and the conductive substrate electrode ES2.

[0019] In the second scheme in FIG. 1b, the viscoelastic layer G isdisposed on the driving electrode structure ES1, which in turn is formedon a glass substrate SM1. The electric field deforming the viscoelasticlayer G is generated by applying alternating voltages to theneighbouring electrode zones in the driving electrode structure ES1.

[0020] In both of the aforementioned schemes, the free surface of theviscoelastic layer G can be coated with a conductive reflecting layer(sputtered metal film).

[0021] According to our best understanding, all the light modulatorstructures presented in the chapter 7 of “Physics of Reliofography” anddiscussed shortly above are based on the basic idea of deforming theviscoelastic layer into a surface structure having a substantiallysinusoidally varying cross-section. This structure can be then utilizedas an electrically controlled sinusoidal grating in order to modulatethe incident light wave. For example, FIGS. 7.1, 7.5 and 7.17 in chapter7 of “Physics of Reliofography” describe devices in which the drivingelectrodes are arranged in the form of evenly spaced parallel stripes inorder to produce a sinusoidally varying grating structure. FIGS. 7.4 and7.27 show devices, where certain separate areas of the viscoelasticlayer are manipulated with separate electrode structures, which eachconsist of electrodes arranged in the form of parallel stripes. Thus, inthe case of FIGS. 7.4 and 7.27, the different areas within the totalarea of said viscoelastic layer can be addressed separately in order toform smaller area sinusoidal gratings.

[0022] The main purpose of the present invention is to produce a novelreconfigurable optical device, which is based on the use of electricallydeformable viscoelastic layer in order to manipulate the light passingthrough said viscoelastic layer, but which is not limited to producingonly sinusoidally varying grating structures. This innovation allowingto manipulate the viscoelastic layer in completely new ways broadenssignificantly the possibilities to use electrically controlledviscoelastic materials for optical switching applications.

[0023] To attain this purpose, the device according to the invention isprimarily characterized in what will be presented in the characterizingpart of the independent claim 1.

[0024] The invention also relates to a method for forming electricallyreconfigurable optical devices. The method according to the invention isprimarily characterized in what will be presented in the characterizingpart of the independent claim 8.

[0025] The basic idea of the invention is to use specific electrodestructures and electrode voltages in order to produce strength and/orspatial distribution of the electric field/s that allow to shape thecross-section of the viscoelastic layer beyond simple sinusoidallyvarying forms. These changes in the cross-sectional shape of theviscoelastic material can be utilized to create a variety of diffractiveoptical structures to accomplish different optical functions.

[0026] In one specific embodiment of the invention, the electrodestructure is arranged to form an electrically configurable blazedgrating. A blazed grating can be used to diffract substantially all ofthe incident light in one direction or to one target (diffraction order)at a time, which provides the possibility to accomplish opticalswitching without significant loss of light. Thus, in this respect, theperformance of a blazed grating is superior compared to a sinusoidalgrating, which diffracts light intrinsically simultaneously at least intwo different diffraction orders (directions).

[0027] In another embodiment of the invention, the electrode structureis arranged to form a switchable Fresnel zone lens. A Fresnel zone lenscan be used for example to focus an incident light beam into a singlefocal point, or to collimate an incident light beam. A Fresnel zone lensaccording to the invention can be utilized as an electricallyreconfigurable lens.

[0028] The devices according to the invention are significantly moreadvantageous than prior art devices in providing much widerpossibilities to manufacture diffractive, electrically reconfigurableoptical devices. The manufacture of such devices also promises to berelatively easy and economical compared to prior art technologiesallowing, for example, the use of a wider variety of substrate materialsand simpler manufacturing processes. The manufacture of the devicesaccording to invention does not involve for example the use ofenvironmentally harmful liquid crystal materials or require deepetching. Further, the optical devices according to the invention areindependent of polarization.

[0029] The preferred embodiments of the invention and their benefitswill become more apparent to a person skilled in the art through thedescription and examples given hereinbelow, and also through theappended claims.

[0030] In the following, the invention will be described in more detailwith reference to the appended drawings, in which

[0031]FIGS. 1a,1 b illustrate prior art light modulator structuresutilizing electrically controlled transparent viscoelastic layer toproduce sinusoidally varying gratings,

[0032]FIG. 2 illustrates the behaviour of dielectric liquid in anelectric field between electrode plates of a field capacitor,

[0033]FIG. 3a/b illustrate schematically a reconfigurable blazed gratingaccording to the invention,

[0034]FIG. 4 illustrates schematically a reconfigurable Fresnel zonelens according to the invention,

[0035]FIG. 5a illustrates schematically an embodiment of the inventionwhere the viscoelastic layer is arranged on the top of the first drivingelectrode structure,

[0036]FIG. 5b illustrates schematically an embodiment of the inventionwhere the viscoelastic layer is arranged opposing the first drivingelectrode structure,

[0037]FIG. 5c illustrates schematically an embodiment of the inventionwhere the viscoelastic layer is sandwiched between the first and secondelectrode structures and arranged opposing the first driving electrodestructure, and

[0038]FIG. 5d illustrates schematically an embodiment of the inventionwhere the viscoelastic layer is sandwiched between the first and secondelectrode structures and arranged on the top of the first drivingelectrode structure.

[0039] It is to be understood that the drawings presented hereinbeloware designed solely for purposes of illustration and thus, for example,not for showing the various components of the devices in their correctrelative scale and/or shape. For the sake of clarity, the components anddetails which are not essential in order to explain the spirit of theinvention have also been omitted in the drawings.

[0040]FIG. 2 illustrates the general principle of physics, which can beobserved with dielectric substances. A dielectric substance can bedefined as a substance in which an electric field may be maintained withzero or near zero power dissipation, i.e. the electrical conductivity iszero or near zero. In an electric field, the surface of two dielectricswith different dielectric constants is known to experience a force whichis proportional to the square of the electric field strength. In FIG. 2where an electric field is formed between electrode plates 20 and 21 ofa field capacitor by applying suitable voltages V₁ and V₂ on saidelectrodes, dielectric liquid 22 is drawn between the electrode platesbecause of the aforementioned force effect.

[0041] Hereinbelow, some specific examples of different types of opticalswitching devices incorporating the electrically controlled viscoelasticlayer are presented. It should be understood that these examples shouldnot be interpreted as a definition of the limits of the invention, butthey are merely intended to clarify the spirit of the invention.

[0042] Various other diffractive optical structures can be realizedaccording to the invention and within the limits of the appended claims.

[0043] Reconfigurable Blazed Grating

[0044]FIGS. 3a and 3 b illustrate the use of the electrically controlledtransparent viscoelastic layer G to create a reconfigurable blazedgrating 30.

[0045] It is generally known in the art that blazed diffraction gratingsare capable of directing the light mainly in only one diffraction orderinstead of spreading the available light energy out over a number oflower-irradiance diffraction orders. Thus, a blazed grating can providea significantly higher light throughput than other types of diffractiongratings.

[0046] Since the force on the dielectric material located in an electricfield depends on the square of the electrical field, it is possible todeform the viscoelastic layer G into a desired structure by using anarray of densely packed electrode zones and by applying appropriatevoltages in said electrode zones.

[0047] In FIGS. 3a and 3 b, the first electrode structure ES1 (drivingelectrodes) consists of electrode zones arranged as substantiallyparallel adjacent stripes. Said electrode zones are further divided intogroups of four adjacent zones, which zones are supplied from the commonvoltage source through voltage-dropping means 31-34. Within each of saidgroups, the individual electrode zones are therefore supplied each witha substantially different voltage.

[0048] In FIGS. 3a and 3 b, the second electrode structure ES2 consistsof a single electrode zone. For the sake of clarity, the substratematerials SM1,SM2 supporting the first and second electrode structuresES1,ES2 are not shown in FIGS. 3a and 3 b.

[0049] By varying the voltage upon the electrode zones of the firstelectrode structure ES1 in a manner which corresponds to the act ofmoving from the situation illustrated in FIG. 3a to that of FIG. 3b, thedirection of the so-called blaze angle of the viscoelastic grating canbe changed and a different diffraction order (direction) can beselected.

[0050] When light diffracted to said different orders (and directions)is arranged to hit different targets, the incident light can be directedto one of said targets without splitting the light between multipletargets. Thus, the switchable blazed grating 30 can be used to passsubstantially all the incident light through without deviation, oralternatively to direct substantially all the light into one of severaltargets.

[0051] By selecting the number and magnitude (potential) of thedifferent voltage levels and the way they are applied to the individualelectrode zones of the first electrode structure ES1, the blaze angleand/or the grating constant of the viscoelastic grating can beelectrically reconfigured.

[0052] Reconfigurable Fresnel Zone Lens

[0053]FIG. 4 illustrates the use of the electrically controlledtransparent viscoelastic layer G to create a reconfigurable Fresnel zonelens 40. A Fresnel zone lens (FZL) is a diffractive optical elementcapable of focusing light by diffracting light from annular concentriczones so that the diffracted light interferes constructively in thefocus. As is well-known in the art, said concentric zones obey therelation:

{square root}{square root over (ρ_(m) ²)}+f ² −f=mλ  (1)

[0054] in which m=number of concentric zones

[0055] ρ_(m)=radii of zone m

[0056] λ=wavelength of the incident light

[0057] f=principal focal length

[0058] In addition to having a single focus at distance of f, the FZLhas other focus points at f/3, f/5, f/7 . . . , which correspond todifferent diffraction orders. The manner in which the light energy isdivided among the different diffraction orders can be affected by theproperties of the concentric zones.

[0059] In FIG. 4, the first electrode structure ES1 (driving electrodes)consists of annular and concentric electrode zones with their number andradii arranged according the aforementioned equation (1). The secondelectrode structure ES2 consists of a single electrode zone. For thesake of clarity, the first and second substrate materials SM1,SM2supporting the first and second electrode structures ES1,ES2 are notshown in FIG. 4.

[0060] When a voltage between the first electrode structure ES1 and thesecond electrode structure ES2 is switched on and off, the Fresnel zonelens 40 is switched between two states: When the voltage is switchedoff, the collimated light beam B incident on the device passes throughthe Fresnel zone lens 40 without being substantially affected. When thevoltage is switched on, the viscoelastic material G is deformed into aFresnel lens which causes the incident light beam B to be focused intoone or more focal points. By arranging the Fresnel zones in a suitablemanner, the Fresnel zone lens 40 can be arranged to have a desired focallength.

[0061] The Fresnel zone lens 40 can be realized as a transparentstructure as illustrated in FIG. 4, or it can also be realized as areflective structure arranging the first ES1 or the second ES2 electrodestructure/s, and/or substrate materials SM1,SM2 supporting saidelectrode structures to be reflective.

[0062] The neighbouring concentric electrode zones in the firstelectrode structure ES1 can be supplied all with a substantially samevoltage as indicated in FIG. 4, but it is also possible to supply someor each of the concentric electrode zones in the first electrodestructure ES1 with individually differing voltages.

[0063] Further, it is also possible to apply alternating voltages toneighbouring electrode zones in the first electrode structure ES1, whicheliminates the need for a separate second electrode structure ES2

[0064] Instead of consisting of annular and concentric electrode zones,the electrode structures may also consist of elliptical, rectangular orpolygonal shaped closed-loop electrodes, which are arrangedconcentrically within each other according to their diameter.

[0065] While the invention has been shown and described above withrespect to selected types of optical switching devices, it should beunderstood that these devices are only examples and that a personskilled in the art could construct other optical diffractive switchingdevices utilizing techniques other than those specifically disclosedherein while still remaining within the spirit and scope of the presentinvention. It should therefore be understood that various omissions andsubstitutions and changes in the form and detail of the switchingdevices illustrated, as well as in the operation of the same, may bemade by those skilled in the art without departing from the spirit ofthe invention. For example, it is expressly intended that allcombinations of those elements which perform substantially the samefunction in substantially the same way to achieve the same results arewithin the scope of the invention. Moreover, it should be recognizedthat structures and/or elements shown and/or described in connectionwith any disclosed form or embodiment of the invention may beincorporated in any other disclosed or described or suggested form orembodiment as a general matter of design choice. It is the intention,therefore, to restrict the invention only in the manner indicated by thescope of the claims appended hereto.

[0066] For example, the layer of the dielectric and transparentviscoelastic material G may be arranged directly on the top of the firstdriving electrode structure ES1, or opposing said first electrodestructure ES1. Such embodiments of the invention are illustratedschematically in FIGS. 5a and 5 b, respectively.

[0067] Depending on the application, optionally, a second electrodestructure ES2 may be located opposing the first electrode structure ES1so that the electric field generated between the first ES1 and secondES2 electrode structures passes through the layer of the viscoelasticmaterial G. In such embodiments of the invention, the viscoelastic layerG becomes sandwiched between the first ES1 and second ES2 electrodestructures as shown schematically in FIGS. 5c and 5 d.

[0068] The use of a second electrode structure ES2 allows to manipulatethe viscoelastic layer G at reduced voltage levels relative to thevoltages required for operation utilizing only the first electrode layerES1. The second electrode structure ES2 also increases the degree offreedom in generating a specified electric field and correspondingcross-sectional shape of the viscoelastic layer.

[0069] However, the use of a separate second electrode structure ES2 isnot necessary if the neighbouring electrode zones in the first drivingelectrode structure ES1 are provided with suitable (favourablyalternating) voltages so that electric fields are generated in betweenthe neighbouring electrode zones.

[0070] The number of the separate electrode zones in the first electrodestructure ES1 or in the second electrode structure ES2 is arbitrary, andthe number can therefore be increased or decreased depending on theparticular optical switching application. The number of the electrodezones in each group formed within the first driving electrode structureES1 is also arbitrary and can also vary between said groups.

[0071] It is also obvious for a person skilled in the art that theoperation of the optical devices according to the invention relies onsome applications on optical interference, and thus requires a certaindegree of coherence and/or collimation of the optical signal/beam thatis being processed.

[0072] By reversing the direction of propagation of light, the operationof the optical devices changes accordingly, for example, instead offocusing the light it becomes collimated.

[0073] The suitable transparent viscoelastic material G includes, forexample, silicone gel, oil, various polymer materials or other viscoussubstances that have a tendency to deform when placed in a presence ofan electric field, and said materials relax towards their original formor shape after the aforementioned effect ceases.

[0074] The transparent electrode structure ES1 and/or ES2 is preferablymade of indium tin oxide (ITO), as is known in the art, and thetransparent substrates SM1,SM2 necessary to support said electrodestructures are preferably made of glass. Other methods for creatingsubstantially transparent electrode structures on any substantiallytransparent substrate material can also be employed without departingfrom the scope of the present invention. Instead of being fullytransparent, it is also obvious that the substrate materials and/orelectrode structures on either side of the viscoelastic layer G may bearranged to be fully or partly reflecting and/or providing spectralfiltering of the transmitted and/or reflected light. It is also obviousthat the free surface of the viscoelastic layer G can be coated with areflecting layer, for example with a metallic film applied by sputteringtechniques.

1. An optical reconfigurable device for diffracting an incident lightwave (B) comprising at least a first transparent driving electrodestructure (ES1) consisting of several electrode zones arranged in amanner that said electrode zones are capable of receiving voltages forgenerating electric field or fields, a layer of dielectric andtransparent viscoelastic material (G) arranged on the top or opposingsaid first electrode structure (ES1) and capable of being deformed inlocal thickness in response to said electric field/s, so that whenincident light wave (B) passes through said viscoelastic material (G),the light wave (B) experiences diffraction according to local variationsin the thickness of the layer of said viscoelastic material (G),characterized in that the arrangement of the individual electrode zonesin said first electrode structure (ES1) complies with one of thefollowing alternatives: said electrode zones of said first electrodestructure (ES1) are grouped into groups composed of two or more adjacentelectrode zones, and within each of said groups, individual electrodezones are supplied each with a substantially different voltage, or saidelectrode zones of said first electrode structure (ES1) aresubstantially annular, elliptical, rectangular or polygonal closed-loopelectrodes arranged within each other according to their diameter, andsaid closed-loop electrode zones are supplied all with a substantiallysame voltage, or some or each of said electrode zones are supplied withindividually different voltages.
 2. The device according to claim 1,characterized in that said device also comprises a second transparentelectrode structure (ES2) consisting of one or more separate electrodezones arranged in a manner that said electrode zones are capable ofreceiving voltages for generating an electric field or fields in amanner that said electric field/s passes through said viscoelasticmaterial (G) from said second electrode structure (ES2) to said firstelectrode structure (ES1).
 3. The device according to claim 1,characterized in that said first (ES1) and/or said second (ES2)electrode structure/s, and/or substrate materials (SM1,SM2) supportingsaid electrode structures is/are arranged to be light reflecting.
 4. Thedevice according to claim 1, characterized in that the substratematerial (SM1) supporting said first electrode structure (ES1) and/orthe substrate material (SM2) supporting said second electrode structure(ES2) is/are arranged to provide spectral filtering of the light wave(B).
 5. The device according to claim 1, characterized in that saidfirst (ES1) and/or second (ES2) electrode structure/s is/are indium tinoxide (ITO) structure/s.
 6. The device according to claim 2,characterized in that said first electrode structure (ES1) consists ofelectrode zones in the form of parallel stripes, said electrode zones ofsaid first electrode structure (ES1) are grouped into groups composed ofseveral adjacent zones, said adjacent zones in said groups are suppliedeach with a different voltage supplied from a common source throughvoltage-dropping means (61,62,63,64), and said second electrodestructure (ES2) consists of a single electrode zone connected to avoltage having substantially opposite polarity than the voltagesconnected to said first electrode structure (ES1), so that saidviscoelastic layer (G) can be deformed to a form having a surfacecross-section to realize an electrically reconfigurable blazed grating(30).
 7. The device according to claim 2, characterized in that saidfirst electrode structure (ES1) consists of electrode zones in the formof annular and concentric closed-loop electrodes connected to a commonvoltage, and said second electrode structure (ES2) consists of a singleelectrode zone connected to a voltage having substantially oppositepolarity than voltages connected to said first electrode structure(ES1), so that said viscoelastic layer (G) can be deformed to a formhaving a surface cross-section to realize an electrically reconfigurableFresnel zone lens (40).
 8. A method for forming a reconfigurable opticaldevice for diffracting an incident light wave (B) comprising at leastthe steps of forming a first transparent driving electrode structure(ES1) consisting of several electrode zones arranged in a manner thatsaid electrode zones are capable of receiving voltages for generatingelectric field or fields; forming a layer of dielectric and transparentviscoelastic material (G) on the top or opposing said first electrodestructure (ES1) and capable of being deformed in local thickness inresponse to said electric field/s, so that when the incident light wave(B) passes through said viscoelastic material (G), the light wave (B)experiences diffraction according to the local variations in thethickness of the layer of said viscoelastic material (G), characterizedin that the individual electrode zones in said first electrode structure(ES1) are arranged to comply with one of the following alternatives:said electrode zones of said first electrode structure (ES1) are groupedinto groups composed of two or more adjacent electrode zones, and withineach of said groups, individual electrode zones are supplied each with asubstantially different voltage, or said electrode zones of said firstelectrode structure (ES1) are substantially annular, elliptical,rectangular or polygonal closed-loop electrodes arranged within eachother according to their diameter, and said closed-loop electrode zonesare supplied all with a substantially same voltage, or some or each ofsaid electrode zones are supplied with individually different voltages.9. The method according to claim 8, characterized in that said methodalso comprises a step of forming a second transparent electrodestructure (ES2) consisting of one or more separate electrode zonesarranged in a manner that said electrode zones are capable of receivingvoltages for generating an electric field or fields in a manner thatsaid electric field/s pass through said viscoelastic material (G) fromsaid second electrode structure (ES2) to said first electrode structure(ES1).
 10. The method according to claim 8, characterized in that saidfirst (ES1) and/or said second (ES2) electrode structure/s, and/orsubstrate materials (SM1,SM2) supporting said electrode structuresis/are arranged to be light reflecting.
 11. The method according toclaim 8, characterized in that the substrate material (SM1) supportingsaid first electrode structure (ES1) and/or the substrate material (SM2)supporting said second electrode structure (ES1) is/are arranged toprovide spectral filtering of the light wave (B).
 12. The methodaccording to claim 8, characterized in that said first (ES1) and/orsecond (ES2) electrode structure/s is/are formed as indium tin oxide(ITO) structure/s.
 13. The method according to claim 9, characterized inthat said first electrode structure (ES1) consists of electrode zones inthe form of parallel stripes, said electrode zones of said firstelectrode structure (ES1) are grouped into groups composed of severaladjacent zones, said adjacent zones in said groups are supplied eachwith a different voltage supplied from a common source throughvoltage-dropping means (61,62,63,64), and said second electrodestructure (ES2) consists of a single electrode zone connected to avoltage having substantially opposite polarity than the voltagesconnected to said first electrode structure (ES1), so that saidviscoelastic layer (G) can be deformed to a form having a surfacecross-section to realize an electrically reconfigurable blazed grating(30).
 14. The method according to claim 9, characterized in that saidfirst electrode structure (ES1) consists of electrode zones in the formof annular and concentric electrodes connected to a common voltage, andsaid second electrode structure (ES2) consists of a single electrodezone connected to a voltage having substantially opposite polarity thanthe voltages connected to said first electrode structure (ES1), so thatsaid viscoelastic layer (G) can be deformed to a form having a surfacecross-section to realize an electrically reconfigurable Fresnel zonelens (40).